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# Drawbacks of Rutherford Atomic Model

Let us first understand about the basics of Rutherford Atomic model.  Before discussing the advantages and disadvantages it is very necessary to understand the basics of Rutherford atomic model.

Initially JJ Thomson presented the plum in a pudding model in which electrons were present in the atom like plum in a pudding. Sir Ernest Rutherford refuted this model to its very core. He conducted the experiment with the use of Gold foil and alpha particles. In this experiment the gold foil was bombarded with alpha particles. To Rutherford’s surprise most of the particles passed straight through the foil. He has a zinc scintillator placed at the back of the foil in order to see scintillations. While most of the particles passed through the foil, some were diverted at an angle of more than 90 degrees, while a very few were reflected back at 180 degrees. This was a very shocking finding because this suggested that most of the mass and hence the charge is present and concentrated in the middle of the atom. This charge is present in a very small region. This was because not many particles were deflected, most of them passed through the gold foil. Also most of the mass of the atom was concentrated in the middle. This region was then called nucleus.

There were many shortcomings or drawbacks of Rutherford atomic model. They are as follows –
1. Rutherford did not mention any direct link between the charge of the nucleus and the atomic mass. He did not mention whether this was half or more than that of atomic mass.
2. He did not mention the relation between charge of the nucleus and atomic number.
3. It was later confirmed that the charge on the nucleus and the atomic number are exactly the same entities.
4. Rutherford model did talk about ‘most’ of the atomic mass (the central nucleus) but did not say anything about the remaining of it.
5. Rutherford did not talk about the rest of the atomic mass and about the exact positioning of electrons. His model just stated that electrons may be arranged in rings (As in Hydrogen ). But this was already stated in JJ Thomson model and hence was nothing new.
6. Also as per Rutherford’s model electrons are charged particles revolving round the nucleus like planets around the sun in solar system. They do so in a circular motion. But if this was true then electrons would also experience acceleration as any other particle revolving in a circular orbit would do. This would lead to energy loss and electrons will fall in nucleus which will in turn cause the atom to be highly unstable. This is false. We know today and knew before that atom is stable.
These shortcomings were the reason for the upcoming new model that is the Bohr’s model of Atom. Bohr model clearly talked about the positioning of electrons in the atom etc. Rutherford experiment with the gold foil also proved that the alpha particles were never affected by the presence of the electrons in the atom. Till now it was realized that atom is a single particle but in subsequent years it was proved by experiments that atom is basically made up of much smaller particles. These particles are today known as neutrons, electrons and protons. Neutrons and protons make up most of the nucleus. Out of this neutrons are mass less and they have neutral charge. However th

From Wikipedia

Rutherford model - Wikipedia, the free encyclopedia

The Rutherford model or planetary model is a model of the atom devised by Ernest Rutherford. Rutherford directed the famous Geiger-Marsden experiment in ...

Bohr model

In atomic physics, the Bohr model, devised by Niels Bohr, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus&mdash;similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. This was an improvement on the earlier cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911). Since the Bohr model is a quantum physics-based modification of the Rutherford model, many sources combine the two, referring to the Rutherfordâ€“Bohr model.

Introduced by Niels Bohr in 1913, the model's key success lay in explaining the Rydberg formula for the spectral emission lines of atomic hydrogen. While the Rydberg formula had been known experimentally, it did not gain a theoretical underpinning until the Bohr model was introduced. Not only did the Bohr model explain the reason for the structure of the Rydberg formula, it also provided a justification for its empirical results in terms of fundamental physical constants.

The Bohr model is a primitive model of the hydrogen atom. As a theory, it can be derived as a first-order approximation of the hydrogen atom using the broader and much more accurate quantum mechanics, and thus may be considered to be an obsolete scientific theory. However, because of its simplicity, and its correct results for selected systems (see below for application), the Bohr model is still commonly taught to introduce students to quantum mechanics, before moving on to the more accurate but more complex valence shell atom. A related model was originally proposed by Arthur Erich Haas in 1910, but was rejected. The quantum theory of the period between Planck's discovery of the quantum (1900) and the advent of a full-blown quantum mechanics (1925) is often referred to as the old quantum theory.

## Origin

In the early 20th century, experiments by Ernest Rutherford established that atoms consisted of a diffuse cloud of negatively charged electrons surrounding a small, dense, positively charged nucleus. Given this experimental data, Rutherford naturally considered a planetary-model atom, the Rutherford model of 1911 â€“ electrons orbiting a solar nucleus â€“ however, said planetary-model atom has a technical difficulty. The laws of classical mechanics (i.e. the Larmor formula), predict that the electron will release electromagnetic radiation while orbiting a nucleus. Because the electron would lose energy, it would gradually spiral inwards, collapsing into the nucleus. This atom model is disastrous, because it predicts that all atoms are unstable.

Also, as the electron spirals inward, the emission would gradually increase in frequency as the orbit got smaller and faster. This would produce a continuous smear, in frequency, of electromagnetic radiation. However, late 19th century experiments with electric discharges through various low-pressure gases in evacuated glass tubes had shown that atoms will only emit light (that is, electromagnetic radiation) at certain discrete frequencies.

To overcome this difficulty, Niels Bohr proposed, in 1913, what is now called the Bohr model of the atom. He suggested that electrons could only have certain classical motions:

1. The electrons can only travel in special orbits: at a certain discrete set of distances from the nucleus with specific energies.
2. The electrons of an atom revolve around the nucleus in orbits. These orbits are associated with definite energies and are also called energy shells or energy levels. Thus, the electrons do not continuously lose energy as they travel in a particular orbit. They can only gain and lose energy by jumping from one allowed orbit to another, absorbing or emitting electromagnetic radiation with a frequency Î½ determined by the energy difference of the levels according to the Planck relation:\Delta{E} = E_2-E_1=h\nu \ , where h is Planck's constant.
3. The frequency of the radiation emitted at an orbit of period T is as it would be in classical mechanics; it is the reciprocal of the classical orbit period: \nu = {1\over T}

The significance of the Bohr model is that the laws of classical mechanics apply to the motion of the electron about the nucleus only when restricted by a quantum rule. Although rule 3 is not completely well defined for small orbits, because the emission process involves two orbits with two different periods, Bohr could determine the energy spacing between levels using rule 3 and come to an exactly correct quantum rule: the angular momentum L is restricted to be an integer multiple of a fixed unit:

L = n{h \over 2\pi} = n\hbar

where n = 1, 2, 3, ... is called the principal quantum number, and Ä§ = h/2Ï€. The lowest value of n is 1; this gives a smallest possible orbital radius of 0.0529&nbsp;nm known as the Bohr radius. Once an electron is in this lowest orbit, it can get no closer to the proton. Starting from the angular momentum quantum rule Bohr was a

Plum pudding model

The plum pudding model of the atom by J. J. Thomson, who discovered the electron in 1897, was proposed in 1904 before the discovery of the atomic nucleus. In this model, the atom is composed of electrons (which Thomson still called "corpuscles", though G. J. Stoney had proposed that atoms of electricity be called electrons in 1894) surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively-charged "plums" surrounded by positively-charged "pudding". The electrons (as we know them today) were thought to be positioned throughout the atom, but with many structures possible for positioning multiple electrons, particularly rotating rings of electrons (see below). Instead of a soup, the atom was also sometimes said to have had a "cloud" of positive charge.

With this model, Thomson abandoned his earlier "nebular atom" hypothesis in which the atom was composed of immaterial vorticies. Now, at least part of the atom was to be composed of Thomson's particulate negative corpuscles, although the rest of the positively-charged part of the atom remained somewhat nebulous and ill-defined.

The 1904 Thomson model was disproved by the 1909 gold foil experiment, which was interpreted by Ernest Rutherford in 1911 to imply a very small nucleus of the atom containing a very high positive charge (in the case of gold, enough to balance about 100 electrons), thus leading to the Rutherford model of the atom. Finally, after Henry Moseley's work showed in 1913 that the nuclear charge was very close to the atomic number, Antonius Van den Broek suggested that atomic number is nuclear charge. This work had culminated in the solar-system-like (but quantum-limited) Bohr model of the atom in the same year, in which a nucleus containing an atomic number of positive charge is surrounded by an equal number of electrons in orbital shells.

Thomson's model was compared (though not by Thomson) to a British dessert called plum pudding, hence the name. Thomson's paper was published in the March 1904 edition of the Philosophical Magazine, the leading British science journal of the day. In Thomson's view: ... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...

In this model, the electrons were free to rotate within the blob or cloud of positive substance. These orbits were stabilized in the model by the fact that when an electron moved farther from the center of the positive cloud, it felt a larger net positive inward force, because there was more material of opposite charge, inside its orbit (see Gauss's law). In Thomson's model, electrons were free to rotate in rings which were further stabilized by interactions between the electrons, and spectra were to be accounted for by energy differences of different ring orbits. Thomson attempted to make his model account for some of the major spectral lines known for some elements, but was not notably successful at this. Still, Thomson's model (along with a similar Saturnian ring model for atomic electrons, also put forward in 1904 by Nagaoka after James C. Maxwell's model of Saturn's rings), were earlier harbingers of the later and more successful solar-system-like Bohr model of the atom.

From Encyclopedia

Atomic Structure Atomic Structure

Question:What can be said about the Rutherford model of an atom based on Newton's laws of motion, the laws of thermodynamics, and the nature of electromagnetic radiation? 1. All of these 2. The electrons are accelerating, so they would be giving off energy. 3. Continuous source of energy must be supplied to the atom. 4. Rutherford model of the atom could not work 5. None of these

Answers:Rutherfords model of the atom couldnt work.

Question:1) They show the exact location of electrons and protons 2)They show empty space between the nucleus and electrons 3)They contain electrons and protons 4)They contain energy levels for electrons which one?

Answers:2. Rutherford's model only showed that there was a nucleus, not protons. Thomson's just showed that electrons existed and that in between was empty space.

Question:a) Calculate the energy of an electron in the second Bohr orbit of a hydrogen atom. b) If the energy difference between the ground state of an atom and its excited stage is 5.4 x 10 (to the power of -19), what is the wavelength of the photon required producing this transition.

Answers:a) The energy of an electron in any orbit is given by En = -13.6/n^2 EV Therefore, energy in second orbit is E2 = - 13.6/4EV = - 3.4 EV b) delta E = 5.4 x 10^-19 (given) Using the formula delta E = hc/Wavelength Rearranging, we have wavelength = hc/deltaE =6.6x10^-34 x 3x10^8 /5.4x10^-19 = 3.66x10^-7m/s

Question:I need an IN-DETAIL description here. I need to make a model of both, but all of the pictures and descriptions I have found so far seem to look exactly the same. WHAT IS THE DIFFERENCE?

Answers:rutherford model just says that whole mass and positive charge of electron is concentrated at its nucleaus the electrons move around nucleaus in elliptical orbit in the same way as planets move around sun modern electron cloud theory says (in addition to above theory ) that trajectory of electron is impossible to determine this theory is completely based on schrodinger's equation. it tells about the most possible arrangements of electron in an atom